Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752440AbbBYDX6 (ORCPT ); Tue, 24 Feb 2015 22:23:58 -0500 Received: from mail-wi0-f173.google.com ([209.85.212.173]:50071 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751848AbbBYDX4 (ORCPT ); Tue, 24 Feb 2015 22:23:56 -0500 MIME-Version: 1.0 In-Reply-To: References: Date: Tue, 24 Feb 2015 22:23:54 -0500 Message-ID: Subject: Re: [PATCH 3.2 055/152] x86_64, switch_to(): Load TLS descriptors before switching DS and ES From: Brian Gerst To: Denys Vlasenko Cc: Andy Lutomirski , Ben Hutchings , Linux Kernel Mailing List , stable , Andrew Morton , Ingo Molnar , Andi Kleen , Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1638 Lines: 39 On Tue, Feb 24, 2015 at 3:08 PM, Denys Vlasenko wrote: > On Tue, Feb 24, 2015 at 9:02 PM, Andy Lutomirski wrote: >>> This currently fails in 32-bit kernels (at least in qemu): >>> >>> / # ./es_test >>> Allocated GDT index 7 >>> [FAIL] ES changed from 0x3b to 0x7b >>> [FAIL] ES was corrupted 1000/1000 times >>> / # uname -a >>> Linux (none) 4.0.0-rc1 #1 SMP Tue Feb 24 16:41:58 CET 2015 i686 GNU/Linux >> >> Want to send a patch? I'll get it in a few days if no one beats me. > > I have no patch, sorry (in fact, I failed to find where is the relevant > 32-bit counterpart). > > It's just security people asked me to backport this and I wondered > maybe I should wait a bit on this one, since fix for 32-bit ought > to appear as well. For 32-bit kernel, userspace DS and ES are saved at syscall/interrupt entry time and reloaded on exit, unlike in 64-bit where they are saved and loaded at context switch time. Therefore 32-bit is not affected by the issue this patch addresses. It looks to me though, that the ES test program doesn't actually test what the patch fixes - the segment attributes, like the base address. It tests just the selector, which shouldn't change across a kernel entry (with a few exceptions, like signals). If the test is failing, then it is a different issue from what this patch addresses. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/